1. Field of the Invention
The present invention relates generally to visual examination apparatus and, more particularly, to an automated visual sensitivity tester for examining the eyes of a human being to determine visual field sensitivity and blind spot size, shape, and position.
2. Description of the Prior Art
Because of the rather substantial dependence of an astronaut on his visual perception and the high degree of likelihood that such perception might change without notice during long term space flight, it is important that vision testing means be provided for enabling him to periodically test and evaluate his visual capabilities.
A test of visual sensitivity during long durations of space flight is important because of the possibility of the occurrence of changes in the transparency of the eye's optic media due to the impingement of various ionizing radiations, foreign matter, or cataract development; changes in the neural, biochemical and/or photochemical processes which underlie visual sensitivity; and changes in the visual perception due to a wide range of retinal and central nervous system dysfunctions which effect sensitivity. In addition, mapping the size, shape, and location of the blind spot is of value not only in determining the state of retinal (thus visual) function near the perimeter of the blind spot, but in providing an indication of changes in intraocular pressure. It is well-known that an intraocular pressure change may indicate such things as the presence of ocular inflammation, changes in blood pressure, elasticity of retinal vessels, body temperature, alkalinity, and osmotic pressure of the cardiovascular system, closure or clogging of the anterior ocular chamber, or variation of the volume of any of the intraocular areas.
Presently, no fully automated visual field testing or blind spot mapping apparatus is commercially available. Although there are available a number of hand-operated visual "perimeters," such as the Goldmann Perimeter and the Feree-Rand B & L Semi-Automatic Recording Perimeter, these devices require that an operator slowly manually move the visual stimulus over the patient's visual field. Furthermore, these devices are difficult to use; require a moderate-to-high degree of operator training in the use of the tester; are relatively expensive; and produce relatively poor correspondence between the test spot's location and its final recorded position in the patient's visual field.
Among the performance criteria for such a vision tester are: adequate sensitivity to changes in visual performance that accompany the various stresses encountered in space flight; sufficient comprehensiveness to detect the possibility of changes in visual functions other than those expected; and adequate diagnostic value--the tester should not only detect a dysfunction, but should provide an indication of the extent of its development.